Implantable cardiac stimulation devices generally include pacing devices, implantable cardiac defibrillation devices and devices that can delivery pacing and defibrillation therapy as appropriate. In general, activation of cardiac tissue occurs in response to current passing through myocardial tissue which causes the tissue to depolarize and contract. Conventional stimulation devices rely on electrode placement and/or selection of an electrode configuration to direct one or more current paths. Choice of electrode configuration is, of course, intimately tied to features of a stimulation device. For example, some conventional stimulation devices include a right ventricular lead only while others include a right ventricular lead and a left ventricular lead yet others may include only a general cardiac lead, a left ventricular lead, etc. While bi-ventricular pacing may be achieved using a variety of devices depending on device specifics, conventional bi-ventricular pacing is usually associated with stimulation devices that include at least one right ventricular lead and at least one left ventricular lead.
Conventional bi-ventricular devices typically achieve right ventricular activation without parasitic or inadvertent stimulation of the left ventricle; however, activation of the left ventricle without parasitic or inadvertent stimulation of the right ventricle has proven more problematic. Further, some individuals experience pain or “pocket stimulation” when too high of a current flows through the case of an implanted device. Of course, such pain or pocket stimulation may be avoided where a selected electrode configuration does not include using the case of the stimulation device as an electrode. Conventional approaches to these issues typically rely on judicious selection of electrode configuration. While selection of a particular electrode configuration may act to minimize or avoid parasitic stimulation, pocket stimulation, etc., such a selection may introduce limits that prevent delivery of an optimum therapy.
Various exemplary mechanisms are disclosed herein which aim to overcome at least some limitations associated with conventional cardiac stimulation devices. In particular, various exemplary mechanisms aim to minimize and/or avoid parasitic stimulation and/or patient pain.